This is a city that imports garbage. Some comes from England, some from Ireland. Some is from neighboring Sweden. It even has designs on the American market.

“I’d like to take some from the United States,” said Pal Mikkelsen, in his office at a huge plant on the edge of town that turns garbage into heat and electricity. “Sea transport is cheap.”

Oslo, a recycling-friendly place where roughly half the city and most of its schools are heated by burning garbage — household trash, industrial waste, even toxic and dangerous waste from hospitals and drug arrests — has a problem: it has literally run out of garbage to burn.

The problem is not unique to Oslo, a city of 1.4 million people. Across Northern Europe, where the practice of burning garbage to generate heat and electricity has exploded in recent decades, demand for trash far outstrips supply. “Northern Europe has a huge generating capacity,” said Mr. Mikkelsen, 50, a mechanical engineer who for the last year has been the managing director of Oslo’s waste-to-energy agency.

Yet the fastidious population of Northern Europe produces only about 150 million tons of waste a year, he said, far too little to supply incinerating plants that can handle more than 700 million tons. “And the Swedes continue to build” more plants, he said, a look of exasperation on his face, “as do Austria and Germany.”

Stockholm, to the east, has become such a competitor that it has even managed to persuade some Norwegian municipalities to deliver their waste there. By ship and by truck, countless tons of garbage make their way from regions that have an excess to others that have the capacity to burn it and produce energy.